3b vocabulary

cells, membranes, & homeostasis

amphipathic

molecules with both hydrophobic and hydrophilic regions

micelle

A spherical structure in which lipids with bulky heads and a single hydrophobic tail are packed

bilayer

A two-layered structure of the cell membrane with hydrophilic “heads” pointing outward toward the aqueous environment and hydrophobic “tails” oriented inward away from water

liposome

An enclosed bilayer structure spontaneously formed by phospholipids in environments with neutral pH, like water

fluid

the ability of membrane lipids to move in the plane of the membrane

cholesterol

is amphipathic, with both hydrophilic and hydrophobic groups being in the same molecule

lipid raft

Lipids assembled in a defined patch in the cell membrane

transporter

A membrane protein that moves ions or other molecules across the cell membrane

receptor

A molecule on cell membranes that detects critical features of the environment

enzyme

A protein that accelerates chemical reactions in biological processes

anchor

A membrane protein that attaches to other proteins and helps to maintain cell structure and shape

integral membrane protein

A protein that is permanently associated with the cell membrane and cannot be separated from the membrane experimentally without destroying the membrane itself.

peripheral membrane protein

A protein that is temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions

transmembrane protein

A protein that spans the entire lipid bilayer

fluid mosaic model

A model that describes the structure of cell membranes as a mosaic of various components, including lipids, proteins, and carbohydrates, which move fluidly within the layer

cell membrane

The membrane that surrounds the cytoplasm of the cell, separating the inside of the cell from the outside of the cell; also called the plasma membrane

homeostasis

The active maintenance of a stable environment within cells and organisms

selectively permeable

the cell membrane lets some molecules in and out freely; it lets others in and out only under certain conditions; and it prevents still other molecules from passing through at all

diffusion

The net movement of molecules from areas of higher to lower concentration as a result of their random thermal motion

passive transport

Movement of substances across a cell membrane by diffusion

facilitated diffusion

Diffusion across a cell membrane through a transmembrane protein, such as a channel or carrier

channel protein

A membrane transporter with a passage that allows the movement of molecules through

carrier protein

A transporter that facilitates movement of molecules across a cell membrane

aquaporin

A protein channel that allows water to cross the cell membrane more readily than by diffusing through the lipid bilayer

osmosis

The net movement of a solvent, such as water, across a selectively permeable membrane toward the side of higher solute concentration

osmotic pressure 

The pressure needed to prevent water from moving from one solution into another by osmosis

active transport

The “uphill” movement of substances against a concentration gradient

primary active transport

Active transport that uses the energy of ATP directly to drive the movement of ions or molecules

secondary active transport

Active transport that uses the energy of an electrochemical gradient to drive the movement of ions or molecules

electrochemical gradient

A gradient that has both electrical and chemical components

contractile vacuole

cellular compartment that takes up excess water and waste products from inside the cell and expels them into the external environment

cell wall

structural layer external to the cell membrane that helps maintain the shape and internal composition of the cell

turgor pressure

Pressure within a cell resulting from the movement of water into the cell by osmosis and the tendency of the cell wall to resist deformation

vacuole

A membrane-bound organelle present in some cells, including plant and fungal cells, that contains fluid, ions, and other molecules

cytoskeleton

An internal protein scaffold that helps cells to maintain their shape and serves as a network of tracks for the movement of substances within cells